The present invention relates to a method of controlling combustion of a direct-injection diesel engine by performing multiple injections by means of a common-rail injection system.
As is known, to reduce air and noise pollution, many countries are issuing increasingly strict standards governing pollutant and noise emissions of vehicle internal combustion engines.
As regards air pollution caused by diesel engines, the main problems arise from the presence, in the exhaust gas, of nitric oxides (NOx), particulate matter, carbon monoxides (CO) and hydrocarbons (HC). Nitric oxides, in particular, are currently held responsible for a high degree of pollution by contributing in the formation and increase in the so-called xe2x80x9cozone gapxe2x80x9d, and by forming, in the presence of sunlight, aggressive products which are both harmful to human beings (eye and skin ailments) and damage various types of material.
To reduce the pollutant emissions of internal combustion engines, in particular nitric oxides, various systems have been proposed, but which have failed to give the desired results.
Some of these employ a DeNox catalyst in conjunction with a postinjection of diesel fuel after the main injection, so that the unburnt diesel fuel mixes with the exhaust gas and participates in the reaction catalyzed by the DeNox catalyst to improve the efficiency of the catalyst.
Such a system, however, simply provides for more effectively reducing nitric oxides, and has no effect whatsoever in reducing other pollutant substances or noise emissions of internal combustion engines.
Alongside the problem of reducing pollution caused by pollutant and noise emissions of internal combustion engines, a strong demand also exists for internal combustion engines of increasingly greater efficiency and performance, and increasingly lower fuel consumption.
It is an object of the present invention to provide a combustion control method for reducing the pollutant emissions and combustion noise, while at the same time improving the efficiency, performance and fuel consumption of diesel engines.
According to the present invention, there is provided a method of controlling the combustion of a direct-injection diesel engine having a common-rail injection system, said method comprising the step of performing, at each engine cycle and in each cylinder of said engine, a first main fuel injection around the end-of-compression top dead center position, and being characterized by also comprising the step of performing, at each engine cycle and in each cylinder of said engine, at least one of a first auxiliary fuel injection before said first main injection, and a second auxiliary fuel injection after said first main injection; said first and said second auxiliary injection being performed close enough to said first main injection to take part, together with the first main injection, in the actual combustion of the fuel.